G0704 Swing Arm ATC

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H-M Supporter - Silver Member
H-M Supporter - Silver Member ($10)
Mar 26, 2018
Hi All,

I should say this right off the bat. I have been going on the project 2+ years now (it keeps falling on the backburner to life) and I've never shared it. There was some interest in another thread so I'm going to post it here. This project is just about done at this point.

I own a G0704 which I converted to CNC back in 2012 when Hoss's plans were the only ones to be found. Like many of us I enjoyed working on the machine more than making parts for anything else. I had completed a number of projects for it and really wanted to try my hand at building an ATC. I had seen a few carousel (umbrella) type units done before but I had never seen a swing arm unit like those oh-so-fancy machining centers. Since I was more interested in the build than getting a functional unit as quickly as possible, I decided to try to build the swing arm.

I decided on a few basic design parameters:
  • 16" drum (which ended up holding 3,6,9,or 18 tools depending on how many pockets were installed)
  • 3-5 second tool to tool time (because why not)
  • integration with mach 3
  • 2" max tool diameter (4" if you leave 2 open pockets)
  • TTS style tool holders
I started the design in Autodesk Inventor and took roughly 2 months to come up with a first draft of the system:
ATC 2.jpg
ATC 3.jpg
ATC 4.jpg
ATC 5.jpg
ATC 6.jpg
ATC 7.jpg
ATC 10.jpg
ATC 14.jpg
ATC 15.jpg
(Sorry for the last two, those are really awful "screen shots")

I'm happy to answer any questions anyone has. I have lots more to write up.


H-M Supporter - Silver Member
H-M Supporter - Silver Member ($10)
Mar 26, 2018
I studied Mechanical and Electrical engineering at school and has access to the school shop which I used to make the parts (the G0704 was at my parents house several states away :frown 2: ). When I came home for holidays, I would always have a list of parts to be made.

ATC 16.jpg
Bearing block for swig arm (aluminum) and Nema 17 gearhead stepper plate
ATC 17.jpg
Magnetic chip guards
ATC 18.jpg
Drilling the through hole (didn't have enough Z clearance)
ATC 19.jpg
ATC 20.jpg
ATC 22.jpg
Boring the through hole for bearing fit
ATC 23.jpg
My collection of TTS style ER20 holders (china ~$13 each if I remember)
ATC 25.jpg
Swing arm mount (done with CNC)
ATC 26.jpg

Back at school I was starting to amass the required parts
ATC 27.jpg

ATC 30.jpg
These bearings and shims became the pivot for the drum which holds the tools
ATC 31.jpg
You can see the assembled pivot in the back, and the swing arm unit in the front. The swing arm is extended by an air cylinder and runs on a short piece of THK linear rail.


H-M Supporter - Silver Member
H-M Supporter - Silver Member ($10)
Mar 26, 2018
Here is the assembled swing arm unit (minus the motor). You can see the pivot sticking off the left side. I had to add a second bearing later on to increase rigidity.
ATC 32.jpg
Another view.
ATC 33.jpg
Close up
ATC 34.jpg
The two set screws in the image below plug access holes to reach a shaft coupling.
ATC 35.jpg
A side view shows the Nema 23 stepper mount (far left) for the drum geneva crank, the UP/DOWN proximity sensors behind the swing arm, and the 4 mounting bolts which attach to the top of the column on the G0704.
ATC 36.jpg
Bottom? view - shows the mounting face for the swing arm
ATC 37.jpg
Another view of the pivot
ATC 38.jpg
Through hole of the pivot. It will carry 4 proximity sensor cables and 2 air lines
ATC 39.jpg



H-M Supporter - Gold Member
H-M Supporter - Gold Member ($25)
Jan 20, 2016
Wow! I am blown away, that thing is incredible! Excellent work and thank you for sharing. I would love to see a video of it in action once it is mounted.


H-M Supporter - Silver Member
H-M Supporter - Silver Member ($10)
Mar 26, 2018
Like many, I needed to add a power drawbar. I chose to build the Hoss style triple air cylinder.
ATC 41.jpg
ATC 42.jpg
ATC 43.jpg
Homework anyone?
ATC 48.jpg
At least it got a good grade!
ATC 49.jpg
The first tool pivot is sitting next to the swing arm.
ATC 50.jpg
ATC 51.jpg


H-M Supporter - Silver Member
H-M Supporter - Silver Member ($10)
Mar 26, 2018
I made a tooling plate at the college shop out of "scrap" aluminum (3/4", 7x24), best idea I ever had. Seriously it saves me so much time. 1/4" dowel pin holes and 3/8-16 tapped holes on an offset 1" grid
ATC 54.jpg
Steel tool pivot (need 17 more of these... ugh)
ATC 55.jpg
The sorta finished pivot. Rigid with hard stops on both ends of its 90 degree travel
ATC 57.jpg
Some rings early on in the project
ATC 56.jpg
The 18 position geneva wheel, cut from powder coated steel. This is actually the second one with a modified profile. Notice the taper at the mouth of each slot and the fillets on all corners. This was designed to prevent the binding that occurred when the original one was placed under load.
What a pain to make. This also has a second bearing in the rear for rigidity
ATC 58.jpg
And the matching crank. A shoulder bolt acts as the drive pin.
ATC 59.jpg
and the back, sitting on a down pin. The lobe sticking off the back registers to an inductive proximity sensor for homing.
ATC 60.jpg



H-M Supporter - Silver Member
H-M Supporter - Silver Member ($10)
Mar 26, 2018
I got some help machining the 12" drum disk which mounts the tools (along the perimeter) The index markers (ring of small tapped holes), home marker (single offset hole), and the geneva wheel (center ring of holes).
ATC 45.jpg
Also the side cover
ATC 46.jpg
And the main cover (the tabs are for rivets if I can't find someone to weld it)
ATC 47.jpg

And here we are today. There's probably a years worth of time spent on code, electrical panel build, and testing which has no pictures. I will write up a description of that if anyone is interested. It is designed to operate with Mach 3 using MODBUS over USB. There are some serious quirks about this, but with care it is a very robust system. I have the program fully functional, including look ahead indexing, but have not yet mounted it to the mill. I have to make the other 17 tool pockets.

After I graduated school I moved into an apartment and started a very busy job. I had no access to a shop of any kind, so all my projects got stalled. I recently moved into a house and have the CNC set up along with a new lathe. Besides the ATC software, I also built a 6 axis AC servo CNC control panel which will end of up on the G0704 as soon as I get to making the new motor mounts. I intend to write up a post on that too.

ATC 53.jpg
ATC 52.jpg

Let me know what you think!

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